This invention relates generally to a method and apparatus for homogenization of a liquid stream and a substantially insoluble component. More particularly, this invention is concerned with a method and apparatus for homogenization of a fluid stream and a substantially insoluble component by the use of cavitating flow.
In the past, various mechanical, hydromechanical and hydrodynamic devices have been employed for the creation of emulsions and colloidal suspensions of a fluid component with a second but substantially insoluble fluid component or a finely divided particulate solid, respectively. A particular problem with the known devices relates to the stability of the resulting emulsion or colloidal suspension. Very frequently, constituents of an emulsion or colloid begin to separate or settle within a short period of time, on the order of a few seconds to a minute, so that usefulness of the emulsion or colloidal suspension is severely limited within a time framework. Moreover, storage for any useful period of time has been essentially impossible because of the separation problem.
Another shortcoming of known devices is the ability to handle large volumetric flow rates, on the order of 100 gallons per hour, for example, with high homogenization efficiency. Moreover, the comparatively inefficient known devices are not suited to on-line applications where there must be a substantially continuous supply of homogenized fluid.
Over the years, various types of homogenizing devices have been made. An example of one such device is disclosed in U.S. Pat. No. 3,744,762 issued July 10, 1973 by W. Schlicht. This device includes an annular gap with radially spaced-apart grooves which cooperate with fluid passing through the channel to create a plurality of cavitation zones in the annular gaps. The annular gap itself is defined by two closely spaced-apart members.
In another known homogenizing device, U.S. Pat. No. 3,937,445 issued Feb. 10, 1976 to V. Agosta, a venturi is designed such that the static pressure of fluid flowing through the venturi throat is reduced below the fluid vapor pressure so that cavitation bubbles are propagated in the throat of the venturi and adjacent to the walls thereof.
In the known cavitating homogenization devices and processes, cavitation occurs adjacent to a solid surface of the apparatus. This juxtaposition of a cavitating flow to a solid surface is quite deleterious to the structure of the apparatus itself; it has long been known in the design of hydrodynamic propellers and underwater bodies that the collapse of cavitation bubbles moving into a region of higher static pressure adjacent to a solid causes substantial damage to that solid surface. More particularly, rapidly reversing pressures on the order of 10,000 atmospheres have been attributed to the collapse of cavitation bubbles. Such reversing pressures in a flow adjacent a solid boundary often may result in erosion and ultimate fatigue failure of the adjacent solid surface.
Another particular difficulty with prior studies of cavitation is the fact that those studies are typically concerned with control or elimination of the cavitating flow regime and have not addressed the useful applications to which cavitation may be put. Thus, a typical approach in cavitation research in the past has been to obtain a low cavitation inception parameter which signals the onset of cavitation in a particular system. To the extent that earlier studies have addressed the manner in which cavitation is fostered, these studies have been concerned with supercavitating flows -- those flows in which a spatially fixed bubble is generated in a dynamic fluid system at a wall.
Aside from the few known attempts at employing cavitation as an homogenization mechanism, there has been activity in using sonic vibration to effect the required intimate intermixing of a dispersed component in a continuous component. Sonic vibration, however, does not produce the pressure magnitudes associated with collapsing bubbles and is not a phenomenon which can be self-induced in a fluid dynamic system.
From the foregoing, it is seen that a need continues to exist for a truly effective homogenization process and apparatus which provides an emulsion or colloidal suspension having an extremely long separation half-life and which uses cavitation but avoids mechanically deleterious interaction with the homogenizing apparatus resulting from the collapse of cavitation bubbles.